ABSTRACT Aging is associated with progressive decline of physiological functions and increased risks for major aging-related diseases. Telomere attrition has been proposed as one of the cellular mechanisms that accompany aging and pathologies related to aging. Critically short telomere length (TL) leads to senescence and is etiologically linked to a range of different human diseases. A growing number of biomedical, epidemiological and population research studies have used telomere length as a biomarker of cellular aging that reflects the cumulative effects of environmental exposures and life experiences as well as a risk factor for major diseases. Of the major methods utilized to determine telomere length, quantitative PCR (qPCR) remains the most suitable for large-scale population studies with hundreds or even thousands of samples, due to its low cost, ease of adoption, low DNA quantity requirement and advantages for high throughput. However, inconsistencies have been reported when qPCR TL assays were repeated for the same samples using different pre-analytical and analytical conditions, highlighting the need for careful methodological study of each step of this process. Sample type selection, sample collection, storage, processing issues and assay procedures have each been identified as import steps that may contribute to assay variability. Systematic studies of how each of these steps impacts the assay is urgently needed to reach a consensus on the best practices for qPCR TL analysis. In this proposal, we plan to optimize the pre-analytical and analytical conditions for qPCR focusing on three specimen types: whole blood, the most commonly used specimen for TL in population-based studies; dried blood spots (DBS), a non-invasive collection method widely used to collect neonatal samples, and saliva, another non-invasive home collection method. We further propose to create a set of fully characterized quality control (QC) DNA samples and a reference standard genomic DNA sample, to be used as shared resources for labs that perform qPCR TL. Finally, we propose to augment telomere length measurement by validating assays for single nucleotide polymorphisms (SNP) associated with TL identified through prior genome-wide association studies (GWAS) and examining whether a genetic sum score (from combining the effects of all SNPs) is associated with longitudinal telomere length change in a pediatric cohort as well as an adult cohort. We realize that sample collection, storage and processing conditions, as well as cross-tissue comparisons are critical for qPCR TL and these issues are addressed by other U01 proposals and the U24 network. As a voting member of the steering committee for the U24, we will fully participate in the U24 network by assaying samples distributed by the U24 and the NIA intramural labs for method comparisons as directed by the committee; and by fully adhering to guidelines and protocols established by the committee.